Formulations to selectively etch silicon-germanium relative to silicon

ABSTRACT

Compositions useful for the selective removal by etching of silicon-germanium-containing materials relative to silicon-containing materials, from a microelectronic device having features containing these materials at a surface, the compositions containing hydrofluoric acid, acetic acid, hydrogen peroxide, and at least one additional acid that will improve performance as measured by one or more of an etching rate or selectivity and are tunable to achieve the required Si:Ge removal selectivity and etch rates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119 of U.S. ProvisionalPatent Application No. 62/484,180, filed Apr. 11, 2017, the disclosureof which is hereby incorporated herein by reference in its entirety forall purposes.

FIELD OF THE INVENTION

The following description relates to compositions and processes forselectively etching silicon-germanium material at a surface of amicroelectronic device substrate, relative to etching a silicon materialat the same surface.

BACKGROUND

For decades, the ongoing trend of reducing the size of features ofmicroelectronic devices, e.g., integrated circuits, has enabledincreased densities of functional features on a range of microelectronicdevices. For example, shrinking transistor size has allowed for anever-increasing number of transistors to be included as part of anintegrated circuit, a memory device, or another microelectronic device,leading to the fabrication of microelectronic devices that exhibitincreased processing capabilities or memory capacity.

Steps of preparing certain microelectronic devices, e.g., integratedcircuits, may include selectively removing silicon-germanium (SiGe)material from a surface that contains the SiGe in combination withsilicon (Si). According to certain example fabrication steps, SiGe maybe used as a sacrificial layer in a structure that also containssilicon. Based on such fabrication steps, advanced device structures maybe prepared, such as silicon nanowires and silicon on nothing (SON)structures. Steps in these processes include epitaxial deposition of astructure of alternating layers of Si and SiGe, followed by patterningand, eventually, selective lateral etching to remove the SiGe layers andgenerate a three-dimensional silicon structure.

In certain specific methods of preparing a field effect transistors(FET) for an integrated circuit, silicon (Si) and silicon-germanium(SiGe) materials are deposited as layers onto a substrate, i.e., as an“epitaxial stack” of Si and SiGe. The layers are subsequently patternedusing standard techniques, such as by use of a standardlithographically-generated mask. Next, a directional isotropic etch maybe useful to laterally etch away the sacrificial SiGe material, leavingbehind a silicon nanowire structure.

SUMMARY

The present invention relates to novel and inventive etchingcompositions and related processes for selectively removing, by etching,a silicon-germanium material relative to silicon-containing material,both of which are present at a surface of an in-process microelectronicdevice that may optionally include other conductive, insulative, orsemiconductive materials (silicon oxide), or a material that is usefulduring another fabrication step such as a barrier layer material (e.g.,silicon nitride).

In the past, the integrated circuit and semiconductor fabricationindustries have used aqueous etching compositions that contain about onepart hydrofluoric acid HF, two parts hydrogen peroxide solution, and sixparts acetic acid (“AA”). Etching compositions made from these threeingredients have been described as providing good etching rates for SiGewith high selectivity to silicon.

These three-part (HF/AA/H₂O₂) compositions have been found not to besuitable for preparing silicon nanowires in a field effect transistorstructure, or for preparing other such delicate and complicatedthree-dimensional structures. One shortcoming of the performance ofthese etching compositions is that the selectivity for etching SiGerelative to silicon diminishes as the amount of germanium in thesacrificial SiGe material is reduced. And at the same time, thesacrificial SiGe is preferred to contain a minimum amount of germanium,so that the sacrificial SiGe material provides the best possible matchfor the silicon features.

Another shortcoming is that these three-part etching compositions tendto require a long time to achieve a stable etch rate “after H2O2addition” (hydrogen peroxide is often added to the three-part etchingcomposition at a point-of-use, see infra).

Additionally, with certain in-process microelectronic devices, one ormore other materials (e.g., SiN_(x) or SiO₂) or other materialsfabricating a microelectronic device, may also be present at a surfacethat contains the SiGe and silicon. Previously-used three-part(HF/AA/H₂O₂) etching composition tend to be relatively effective to etchthese other materials, possibly due to the high amount of HF used inthese systems. But preferred methods of etching the device would desireto minimize etching of these other materials. In preferred methods ofselectively etching SiGe located on a surface that contains siliconalong with silicon nitride or silicon oxide, the etching composition andits method of use can preferably exhibit a reduced, inhibited, orminimum rate of removal of the silicon nitride, silicon oxide, or both.An etching composition that contains a high concentration ofhydrofluoric acid would not be expected to be suitable for etching asubstrate that also has exposed silicon nitride or exposed siliconoxide.

In preferred etching compositions of the present invention, the one ormore additional acids included in an etching composition that containsHF/AA/H₂O₂, can be effective to produce a composition that alleviatesone or more of these shortcomings of the three-part etchingcompositions. When used in a method of etching a microelectronic devicesurface that contains silicon and silicon-germanium features at asurface, the inventive etching compositions can exhibit desired, useful,or advantageous performance relative to a comparable etchingcomposition. One example of a comparable etching composition is anetching composition that contains (by weight percent) 11:22:67 HF(49%):AA (99%):H₂O₂ (30%) and no other ingredients. A different exampleof a comparable etching composition is an etching composition that is anotherwise identical HF/AA/H₂O₂ etching composition but that does notinclude one or more additional acids as described herein, e.g., formicacid, sulfuric acid, lactic acid, or a combination of two or more ofthese. The improved performance can be measured as one or more of:selectivity of etching silicon-germanium relative to silicon; desirablyincreased silicon-germanium etch rate; a desirably reduced silicon etchrate; a low etch rate of silicon oxide, silicon nitride, or both. Alsopreferably, an inventive process that uses an inventive etchingcomposition can exhibit an improved (reduced) amount of time to achievean etch rate of SiGe that is 90 percent of a maximum etch rate of SiGethat is eventually achieved by the inventive process.

With more specificity, example etching compositions used in an inventivemethod of etching a substrate that contains silicon andsilicon-germanium structures at a surface can exhibit selectivity inetching silicon-germanium relative to silicon that is improved ascompared to a comparable etching method performed on an identicalmicroelectronic device substrate and using the same conditions and thesame equipment, with the only difference being that the etching solutionof the comparable etching method does not contain any added acidingredient and contains only a combination of HF, AA, and hydrogenperoxide in the same relative amounts as does the inventive etchingcomposition. Alternately, the improvement can be measured against acomparable etching method that uses an etching composition that contains11:22:67 HF (49%):AA (99%):H₂O₂ (30%), with each of the componentsspecified by weight % in water and the relative amounts specified byweight. Selectivity is a ratio of a removal rate of one material (e.g.,silicon-germanium) to a removal rate of a second material (e.g.,silicon). According to preferred inventive etching methods as described,using an inventive etching composition that contains HF, AA, hydrogenperoxide, and one more additional acids as described, the selectivity ofthe removal of silicon-germanium to silicon can be increased if the SiGeetch rate is increased relative to the Si etch rate.

Alternately or in addition, example etching compositions used in aninventive method of etching a microelectronic device substrate thatcontains silicon and silicon-germanium structures at a surface canexhibit an etch rate of silica-germanium that is improved (increased)relative to a comparable etching method performed on an identicalmicroelectronic device substrate and using the same conditions and thesame equipment, with the only difference being that the etching solutionof the comparable etching method does not contain any added acidingredient and contains only a combination of HF, AA, and hydrogenperoxide in the same relative amounts as does the inventive etchingcomposition. Alternately, the improvement can be measured against acomparable etching method that uses an etching composition that contains(by weight percent) 11:22:67 HF (49%):AA (99%):H₂O₂ (30%).

Etch rate is known performance measure of an etching process and can bereported in terms of an amount of material (e.g., in thickness) removedper time (e.g., nanometers of material per minute). Useful methods ofdetermining etch rate of silicon-germanium can be performed by etching asubstrate that includes silicon-germanium at a surface. An examplesubstrate may include an epitaxial layer of silicon-germanium disposedon silicon. Any method of measuring an amount of etching may beeffective, with spectroscopic ellipsometry being one useful andpreferred method for measuring silicon-germanium etch rate.

According to preferred inventive etching methods as described, using aninventive etching composition that contains HF, AA, hydrogen peroxide,and one more additional acids as described, an etch rate ofsilicon-germanium can be increased by at least 10, 20, 50, 60, 80, oreven 100 percent compared to the etch rate of a comparable etchingmethod; for example if a comparable etching method exhibits asilicon-germanium etch rate of 20 nanometers per minute, the improvedmethod can exhibit a silicon-germanium etch rate of at least 22, 24, 30,32, 36, or 40 nanometers per minute, i.e., an increase of 10, 20, 50,60, 80, or even 100 percent from the etch rate of 20 nanometers perminute achieved by the comparable method.

Alternately or in addition, example etching compositions used in aninventive method of etching a microelectronic device substrate thatcontains silicon and silicon-germanium structures at a surface canexhibit an etch rate of silicon that is improved (decreased) relative toa comparable etching method performed on an identical microelectronicdevice substrate and using the same conditions and the same equipment,with the only difference being that the etching solution of thecomparable etching method does not contain any added acid ingredient andcontains only a combination of HF, AA, and hydrogen peroxide in the samerelative amounts as does the inventive etching composition. Alternately,the improvement can be measured against a comparable etching method thatuses an etching composition that contains 11:22:67 HF (49%):AA(99%):H₂O₂ (30%) (by weight percent).

Useful methods of determining etch rate of silicon can be performed byetching a substrate that includes silicon-on-insulator (SOI) at asurface. Any method of measuring an amount of etching may be effective,with spectroscopic ellipsometry being one useful and preferred methodfor measuring silicon etch rate.

According to preferred inventive etching methods as described, using aninventive etching composition that contains HF, AA, hydrogen peroxide,and one more additional acids as described, an etch rate of silicon canbe decreased by at least 10, 20, or 30 percent, compared to the etchrate of a comparable etching method; for example if a comparable etchingmethod exhibits a silicon etch rate of not greater than 2 nanometers perminute, the improved method can exhibit a silicon etch rate of notgreater than 1.8, 1.6, or 1.4 nanometers per minute, i.e., a decrease of10, 20, or 30 percent relative to the etch rate of not greater than 2nanometers per minute achieved by the comparable method.

Alternately or in addition, example etching compositions used in amethod of etching a microelectronic device substrate that containssilicon and silicon-germanium structures at a surface can achieve a 90percent SiGe etch rate in a time that is substantially less than theamount of time that is required for a comparable etching method (asdescribed herein) to achieve a 90 percent SiGe etch rate. A maximum etchrate can be identified by measuring etch rate, versus the elapsed timeof the etching step (i.e., amount of material removed from a surface indistance/time, during the time following the beginning of the etchingstep, which coincides with a time at which hydrogen peroxide is added toacid ingredients to form the etching composition). A maximum etch rate,also referred to as a “stable etch rate” is a rate of removal by etchingof a particular material of a substrate surface, achieved during anetching step (or process), at a time during the etching step at whichthat rate has become substantially constant, i.e., the etch rate ischanging by less than 10% during the following 1 hour period;alternately, a maximum etch rate may be considered to be an etch rate ofthe process at a time of 4 hours after an etching procedure begins, atwhich time hydrogen peroxide is mixed with the other dissolved (acid)materials of the etching composition and applied to the surface. A 90percent etch rate is a rate that is 90 percent of the maximum etch rate.

According to preferred inventive etching methods as described, using aninventive etching composition that contains HF, AA, hydrogen peroxide,and one more additional acids as described (e.g., formic acid, sulfuricacid, lactic acid, or a combination of these), the inventive method canreach a SiGe etch rate that is 90 percent of a maximum SiGe etch rate,in an amount of time that is 10, 20, 30 or 50 percent less than (i.e.,more sooner than) the amount of time required for a comparable etchingmethod to achieve its own 90 percent of maximum SiGe etch rate. Forexample if a comparable etching method achieves a 90 percent of maximumSiGe etch rate in 120 minutes, the improved and inventive method canachieve a 90 percent of maximum SiGe etch rate in 108 minutes or less,96 minutes or less, 84 minutes or less, or 60 minutes or less, i.e., adecrease of 10, 20, 30 or 50 percent relative to 120 minutes required bythe comparable method to achieve a 90 percent etch rate. These amountsof time (e.g., in minutes, hours, etc.) required to achieve a 90 percentof maximum etch rate are independent of the value of the maximum etchrate (having units of, e.g., nanometers per minute).

Alternately or in addition, example etching compositions used in aninventive method of etching a microelectronic device substrate thatcontains silicon and silicon-germanium structures at a surface, as wellas one or more other material such as silicon nitride or silicon oxide,can exhibit an etching rate of the silicon nitride or silicon oxide (orboth) that is improved (decreased) relative to a comparable etchingmethod performed on an identical microelectronic device substrate andusing the same conditions and the same equipment, with the onlydifference being that the etching solution of the comparable etchingmethod does not contain any added acid ingredient and contains only acombination of HF, AA, and hydrogen peroxide in the same relativeamounts as does the inventive etching composition. Alternately, theimprovement can be measured against a comparable etching method thatuses an etching composition that contains (by weight percent) 11:22:67HF (49%):AA (99%):H₂O₂ (30%).

According to preferred inventive etching methods as described, using aninventive etching composition that contains HF, AA, hydrogen peroxide,and one more additional acids as described, an etch rate of siliconnitride, silicon oxide, or both, can be decreased by at least 10, 20, or30 percent, compared to the etch rate of a comparable etching method;for example if a comparable etching method exhibits a silicon nitride orsilicon oxide etch rate of not greater than 2 nanometers per minute, theimproved method can exhibit a silicon nitride or silicon oxide etch rateof not greater than 1.8, 1.6, or 1.4 nanometers per minute, i.e., adecrease of 10, 20, or 30 percent relative to the etch rate of notgreater than 2 nanometers per minute achieved by the comparable method.

An amount of a chemical material such as acid or hydrogen peroxide thatis dissolved in an aqueous etching composition, i.e., a solution, can bedescribed on a basis of parts by weight of the dissolved material perparts by weight (e.g., per 100 parts by weight) of a total amountdissolved materials in the etching composition that contains thedissolved materials. This (parts by weight) basis for reporting amountsand relative amounts of dissolved materials in an aqueous etchingcomposition is a convenient basis for reporting amounts and relativeamounts of these dissolved materials because this basis relates only tothe amount and relative amounts of the dissolved materials and isindependent of the amount of water in the solution. This parts by weightbasis, therefore, conveniently defines the amounts and relative amountsof dissolved chemical materials of the etching composition relative toeach other and not based on a concentration relative to water. Therelative amounts of the dissolved chemical materials will not changebased on a higher or lower amount of water in the etching composition.

When an aqueous etching composition that contains dissolved ingredientsis prepared by combining two or more aqueous ingredients (solutions)such as a combination of two or more aqueous acids solutions with ahydrogen peroxide solution, with each aqueous ingredient containing aknown concentration of dissolved chemical material, the amount ofdissolved ingredient present in the combined solution (on a relativeparts by weight basis) will be the amount (by weight) of the dissolvedingredient in the aqueous ingredient that is used prepare the combinedsolution, per the total amount of all dissolved ingredients from allingredients that are used to prepare the combined solution. The valuescan be normalized to be based on a total of 100 parts by weightdissolved materials.

On this basis, amounts and relative amounts of dissolved chemicalmaterials of an etching composition can be calculated as the weightpercent of the dissolved chemical material (e.g., acid or hydrogenperoxide) that is present in an acid or hydrogen peroxide solution thatis an ingredient of the etching composition, multiplied by the amount(e.g., volume or mass) of that ingredient that is included in theetching composition, divided by the total amount of all such dissolvedingredients used to prepare the etching composition.

As an example, etching compositions may be prepared from ingredientssuch as the following three: 1) 11 parts by weight of 49 percent byweight hydrofluoric acid (HF) solution; 67 parts by volume of 99 percentby weight of acetic acid, and 22 parts by volume of 30 percent by weightof hydrogen peroxide. The 11 parts by weight of the 49 percent HFingredient contribute 5.39 parts by weight of dissolved hydrofluoricacid to the etching composition. The 67 parts by weight of the 99percent acetic acid ingredient contribute about 66.33 parts by weight ofdissolved acetic acid to the etching composition. And the 22 parts byweight of the 30 percent hydrogen peroxide ingredient contribute about6.6 parts by weight of dissolved hydrogen peroxide to the etchingcomposition. The total amount of dissolved ingredients is 78.3 parts byweight (5.4 parts by weight dissolved HF, 66.3 parts by weight dissolvedacetic acid, and 6.6 parts by weight dissolved hydrogen peroxide). Thebalance, 22.68 parts by weight, is water.

The amount of dissolved chemical material, reported on a parts by weightdissolved chemical material per 100 parts by weight of total dissolvedmaterials in the etching composition, is as follows: about 6.89 parts byweight dissolved HF (5.4 parts dissolved HF per 78.3 parts by weighttotal dissolved ingredients); about 84.7 parts by weight dissolvedacetic acid (66.3 parts dissolved HF per 78.3 parts by weight totaldissolved ingredients); and about 8.43 parts by weight dissolvedhydrogen peroxide (6.6 parts dissolved hydrogen peroxide per 78.3 partsby weight total dissolved ingredients).

In one aspect, the invention relates to a method of selectively removingsilicon-germanium from a surface of a microelectronic device relative toa silicon-containing material. The method includes: providing amicroelectronic device surface that includes silicon andsilicon-germanium; providing an aqueous etching composition comprising:hydrogen fluoride, dissolved hydrogen peroxide, dissolved acetic acid,dissolved formic acid, and dissolved sulfuric acid; and contacting thesurface with the silicon-germanium-selective etching composition fortime and at a temperature effective to selectively removesilicon-germanium relative to the silicon.

In another aspect the invention relates to an etching composition forselectively removing silicon-germanium from a surface of amicroelectronic device relative to silicon. The composition comprises:hydrogen fluoride, dissolved acetic acid, dissolved formic acid, anddissolved sulfuric acid, in water.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows steps of microelectronic fabrication, including a step ofselective SiGe etching as described herein. This figure is not to scaleand is schematic.

FIG. 2 shows example data of etch rate versus time after mixing of anetching composition.

FIG. 3 shows a flow diagram of a method of preparing and using anetching composition.

DETAILED DESCRIPTION

The present invention relates to novel and inventive etchingcompositions and related novel and inventive processes for selectivelyremoving, by etching, silicon-germanium from an in-processmicroelectronic device surface that contains structures made ofsilicon-germanium, and of silicon. The surface may optionally alsoinclude other conductive, insulating (e.g., silicon oxide), orsemiconducting materials, or one or more materials known to be usefulduring processing of a microelectronic device, such as a barrier layermaterial (e.g., silicon nitride).

The term “microelectronic device” (or “microelectronic devicesubstrate,” or simply “substrate”) is used herein in a manner that isconsistent with the generally understood meaning of this term in theelectronics, microelectronics, and semiconductor fabrication arts, forexample to refer to any of a variety of different types of:semiconductor substrates; integrated circuits; solid state memorydevices; hard memory disks; read, write, and read-write heads andmechanical or electronic components thereof; flat panel displays; phasechange memory devices; solar panels and other products that include oneor more solar cell devices; photovoltaics; and microelectromechanicalsystems (MEMS) manufactured for use in microelectronic, integratedcircuit, energy collection, or computer chip applications. It is to beunderstood that the term microelectronic device can refer to anyin-process microelectronic device or microelectronic device substratethat contains or is being prepared to contain functional electronic(electrical-current-carrying) structures, functional semiconductorstructures, and insulating structures, for eventual electronic used in amicroelectronic device or microelectronic assembly.

As used herein, the term “silicon” refers to various types ofcrystalline silicon, including Si, polycrystalline Si, and (preferably)monocrystalline Si. The silicon may be present in any structure (i.e.,substrate) that is known or that is useable as a substrate or structurefor making a microelectronic device by steps of semiconductorfabrication, including in the form of silicon-on-insulator (SOI) wafersthat may be used, for example, as a substrate or part of a substrate forof an electronic device such as a field-effect-transistor (FET) or anintegrated circuit or other microelectronic device that contains afield-effect-transistor. The silicon is made substantially of one ormore crystals of silicon atoms that may be may be p-doped, n-doped, orneither, and may contain dopant or other impurities in an amount that issufficiently low to be acceptable for preparing a microelectronicdevice.

The term “silicon-germanium” (or “SiGe”) is used herein in a manner thatis consistent with the meaning of this term in the semiconductor andmaterials arts. These silicon-germanium materials may containessentially only silicon and germanium atoms, in a crystal latticestructure, and do not require any other atomic constituents. Therelative amounts of silicon atoms to germanium atoms may be as desired.But for microelectronic devices and methods of processingmicroelectronic devices as described herein, the amount (concentration,on an atomic basis) of germanium atoms will be substantially lower thanthe amount (concentration) of silicon atoms in the silicon-germaniummaterial. In processes that involve the use of silicon-germanium as asacrificial material to produce silicon structures (e.g., siliconnanowires), the sacrificial silicon-germanium material can preferably beas similar as possible, compositionally, to the silicon in compositionand with respect to physical properties. In specific, it is desired touse as little germanium as possible in a silicon-germanium sacrificialmaterial. In processes that use silicon-germanium as a sacrificialmaterial in combination with silicon as a non-sacrificial material, itcan be desirable for the silicon-germanium material to have acomposition and properties that are as closely matched as possible tothe silicon. A closely-matched sacrificial material can result in thehighest quality structural and performance features of the siliconstructures, after the silicon-germanium is selectively removed byetching. Normally, and preferably, sacrificial silicon-germanium for usein a method as described can include less than 50 percent (atomic)germanium, e.g., less than 30, 25, 20, 15, or 10 atoms germanium per 100total atoms of germanium and silicon. Preferred silicon-germanium foruse as sacrificial silicon-germanium in a method as described herein maybe described as having the formula:Si_(x):Ge_(y)wherein x is in a range from about 0.70 to 0.90; y is in a range fromabout 0.10 to about 0.30; and x+y=1.00. The SiGe may optionally ben-doped or p-doped, but for use of SiGe material as sacrificialmaterial, doping is not necessary. The SiGe may contain dopant or otherimpurities in an amount that is not too high to be acceptable forpreparing a microelectronic device.

Example inventive etching compositions as described can be in the formof an aqueous solution that contains dissolved materials (dissolved inwater of the etching composition), the dissolved materials comprising,consisting of, or consisting essentially of: hydrogen fluoride (HF),dissolved acetic acid (i.e., CH₃CO₂H, hydrogen acetate, ormethanecarboxylic acid, sometimes referred to herein as “AA”), anddissolved hydrogen peroxide (H₂O₂), as well as one or more additionaldissolved acids that improve performance of the etching composition,e.g., formic acid, lactic acid, sulfuric acid, or a combination ofthese. These acid and hydrogen peroxide materials are dissolved in anamount of water of the etching composition.

As a general convention throughout the present description, acomposition or ingredient (e.g., acid solution) that is said to “consistessentially of” water and a dissolved material or a group of listeddissolved materials refers to a composition or ingredient that containsthe water and the dissolved material or group of listed dissolvedmaterials, with not more than an insignificant amount of other dissolvedor un-dissolved (non-aqueous) materials, e.g., not more than 5, 2, 1,0.5, 0.1, or 0.05 parts by weight of another dissolved or un-dissolvedmaterial other than the identified dissolved materials. For example, anetching composition that contains dissolved (non-aqueous) materials thatconsist essentially of: hydrogen fluoride (HF), dissolved acetic acid,dissolved hydrogen peroxide (H₂O₂), and one or more additional dissolvedacids that improve performance of the etching composition, e.g., formicacid, lactic acid, sulfuric acid, or a combination of these, means acomposition that contains these ingredients and not more than 5, 2, 1,0.5, 0.1, or 0.05 parts by weight of any other dissolved or un-dissolvedmaterial or materials (individually or as a total) other than theidentified dissolved materials (hydrogen fluoride (HF), dissolved aceticacid, dissolved hydrogen peroxide (H₂O₂), and one or more additionaldissolved acids that improve performance of the etching composition,e.g., formic acid, lactic acid, sulfuric acid, or a combination ofthese).

In use, the dissolved acid and hydrogen peroxide materials may beprovided in a single “point-of-use composition,” which is a compositionthat is provided and optionally prepared at a location and time at whichthe etching composition will be used by a user, e.g., in a semiconductorfabrication process, to etch an in-process microelectronic device toselectively remove silicon-germanium from a surface of the device thatcontains silicon-germanium, silicon, and optionally other exposedfeature made of other materials such as silicon nitride or siliconoxide.

Optionally, and preferably, an etching composition that is apoint-of-use composition can be prepared by combining aqueous acidmaterials with the hydrogen peroxide, at or near the time of use, i.e.,“at a point-of-use.” Desirably, hydrogen peroxide may be held and storedseparately from acid ingredients, and may be added to the acidingredients at a time before the etching composition is to be used in aprocess or etching a microelectronic device, such as not more than 3hours, 2 hours, 1 hour, or 0.5 hours before using the etchingcomposition. This invention allows for reduced time for stable etchinghigh selective removal of Si_(x)Ge_(y) relative to Si.

The acid ingredients of an etching composition may be combined at apoint-of-use by combining each of the different separate acidingredients at the point-of-use, although combining the acid ingredientsat a point-of-use is not normally preferred. Instead, preferably, asingle composition, i.e., solution, of all of the acid materials (i.e.,an “aqueous acids composition”) can be previously prepared. This aqueousacids composition can be a single composition that contains alldissolved acid materials of an etching composition, in water. Theaqueous acids composition can be prepared by combining: an aqueoushydrofluoric acid solution; an aqueous or concentrated acetic acidsolution or non-aqueous acetic acid composition; and one or more ofaqueous formic acid solution, aqueous sulfuric acid solution, and anamount of lactic acid or lactic acid solution. A preferred aqueous acidscomposition can contain water and dissolved acid materials that consistof or consist essentially of hydrofluoric acid; dissolved acetic acid;dissolved hydrogen peroxide; and one or more of dissolved formic acid,dissolved sulfuric acid, dissolved lactic acid, or two or more of theseadditional dissolved acid materials.

Advantageously, combining aqueous acid ingredients (e.g., in the form ofan aqueous acids composition), with the hydrogen peroxide at or justbefore the composition is to be used in an etching process, allows theetching composition to be used at a time when reactions between hydrogenperoxide and dissolved acid materials, e.g., dissolved formic acid anddissolved acetic acid, have just begun to occur.

Hydrogen peroxide can be reactive with one or more of the dissolvedacids present in an etching composition as described herein, e.g.,acetic acid and formic acid. Hydrogen peroxide can react with aceticacid to produce per-acetic acid ((H₃CC(O)OOH) (peroxyacetic acid, aceticperoxide, acetyl hydroperoxide, proxitane):H₃CC(O)OH+H₂O₂↔H₃CC(O)OOH+H₂O

Hydrogen peroxide can also react with formic acid to produce per-formicacid ((HC(O)OOH) (hydroperoxyformaldehyde, formyl hydroperoxide,permethanoic acid, peroxyformic acid):HC(O)OH+H₂O₂↔HC(O)OOH+H₂O

Without being bound by theory, it is believed that the presence ofper-acetic acid and per-formic acid in an etching composition of thepresent description, at a point-of-use and during a step of etching amicroelectronic device substrate as described, may be responsible for atleast some of the desired performance benefits of an etching compositionof the present description. In specific, the presence of per-acetic acidor per-formic acid in an etching composition, during an etching step,especially during an early portion of the etching step, is believed toreduce the amount of time required for the process to achieve asilicon-germanium etch rate that is 90 percent of a maximumsilicon-germanium etch rate achieved during the etching step.

Improved performance of an inventive composition and method can bemeasured relative to the performance of an otherwise identical etchingcomposition, i.e., a “comparable etching composition,” that is identicalto an inventive etching composition except that the comparable etchingcomposition does not contain any additional acid material as describedherein. Alternately, improved performance can be measured against acomparable etching method that uses a comparable etching compositionthat contains (by weight percent) 11:22:67 HF (49%):AA (99%):H₂O₂ (30%)without any other ingredients. The inventive etching compositions andmethods exhibit improved performance relative to a comparable methodthat is performed on an identical substrate, using identical equipmentand conditions, and using a comparable etching composition as described.

An etching composition as described includes hydrogen fluoride, i.e.,dissolved hydrogen fluoride. The hydrogen fluoride can be provided inthe etching composition in the form of aqueous hydrofluoric acid as aningredient used to prepare the etching composition. Hydrofluoric acid isa known acid material made of hydrogen fluoride (HF) dissolved in water.Hydrofluoric acid is available in a range of concentrations of hydrogenfluoride dissolved in water. A hydrofluoric acid solution of any usefulHF concentration may be used as an ingredient to prepare an etchingcomposition as described, by combining the HF solution with otheringredients such as acetic acid, hydrogen peroxide solution, etc., inany amount that will provide a desired amount of dissolved hydrogenfluoride in the etchant composition, e.g., an amount effective incombination with the other ingredients to produce a useful etchingcomposition as described.

A useful or preferred etching composition as described can contain anyuseful or desired amount of dissolved hydrogen fluoride. Preferredetching composition can include a relatively reduced amount of hydrogenfluoride as compared to previous etching compositions that contain acombination of HF, AA, and H₂O₂, when described on a basis of totaldissolved materials of the etching composition. For example, a usefuletching composition may contain less than 10 parts by weight dissolvedhydrogen fluoride based on 100 parts by weight of dissolved materials inthe etching composition, such as less than 8, 5, or 3 parts by weight HFbased on 100 parts by weight dissolved materials in the composition.Optionally, a preferred etching composition may contain less than 2 orless than 1 part by weight HF based on 100 parts by weight dissolvedmaterials in the composition. These amounts describe the amount ofdissolved hydrogen fluoride present in the etching composition at a timeat which or soon after which hydrogen peroxide is combined with the acidingredients to form a “point-of-use composition.”

Desirably, the reduced amount of hydrogen fluoride in an etchingcomposition may be effective to control an etch rate of silicongermanium, meaning to avoid an etch rate of silicon-germanium that istoo rapid. An etch rate that is too fast can reduce quality of aprocessed microelectronic device. A reduced amount of hydrogen fluoridecan also avoid an etch rate of SiN_(x) or SiO₂ that is too high. HF hasa strong ability to etch SiN_(x) and SiO₂. According to preferredetching compositions and methods of the present description, the etchrate of SiN_(x) or SiO₂ can be relatively low, to allow the inventivecompositions and methods to be useful to process microelectronic devicesthat include structures at their surfaces that are made of SiN_(x) orSiO₂, without causing excess removal of the SiN_(x) or SiO₂.

The etching composition also contains hydrogen peroxide (i.e., H₂O₂,dioxidane, oxidanyl, or perhydroxic acid), i.e., dissolved hydrogenperoxide. The dissolved hydrogen peroxide can be provided in the etchingcomposition in the form of aqueous hydrogen peroxide solution, as aningredient used to prepare the etching composition. Hydrogen peroxide isa known chemical material and is often contained in an aqueous solutionof the hydrogen peroxide dissolved in water. Aqueous hydrogen peroxidesolutions are available in a range of concentrations of the hydrogenperoxide dissolved in water, including concentrations in a range from 1,5, 10 percent hydrogen peroxide, up to 20, 30 or 40 percent, or higher,hydrogen peroxide dissolved in water (on a weight (grams) per volume(liter)) basis). A hydrogen peroxide solution of any usefulconcentration may be used as an ingredient to prepare an etchingcomposition as described, by combining the hydrogen peroxide solutionwith other ingredients such as hydrofluoric acid (aqueous solution),acetic acid solution, etc., as described. The hydrogen peroxide canpreferably be added to other ingredients of the etching composition at apoint-of-use. The hydrogen peroxide solution can contain anyconcentration of dissolved hydrogen peroxide that will be effective tocombine the hydrogen peroxide solution with the other ingredients of anetching composition to produce a useful etching composition asdescribed, containing a desired amount of dissolved hydrogen peroxide.

A useful or preferred etching composition as described can contain anyuseful or desired amount of dissolved hydrogen peroxide. Preferredetching compositions can contain a relatively increased amount ofdissolved hydrogen peroxide as compared to previous etching compositionsthat contain a combination of HF, AA, and H₂O₂, when described on abasis of total (or 100 parts by weight) dissolved materials of theetching composition. For example, a useful etching composition maycontain at least 10, 12, 15, 20, 25 or at least 30 or 35 parts by weightdissolved hydrogen peroxide based on 100 parts by weight dissolvedmaterials in the composition.

These amounts describe the amount of dissolved hydrogen peroxide presentin an etching composition at a time at which or soon after which thehydrogen peroxide is combined with dissolved acid materials to form a“point-of-use composition.” Hydrogen peroxide is known to be reactivewith certain dissolved acid materials that may be present in the etchingcomposition such as dissolved acetic acid and dissolved formic acid. Theamount of hydrogen peroxide that is added to an etching composition thatcontains these dissolved acid materials may decrease as the hydrogenperoxide contacts and reacts with those dissolved acid materials.

The etching composition also contains acetic acid (i.e., CH₃CO₂H,hydrogen acetate, or methanecarboxylic acid, sometimes referred toherein as “AA”), i.e., dissolved acetic acid. The dissolved acetic acidcan be provided in the etching composition in the form of aqueous aceticacid solution, or substantially non-aqueous (e.g., 99 percent) aceticacid, as an ingredient used to prepare the etching composition. Aceticacid is a known acid material made of acetic acid (CH₃CO₂H, hydrogenacetate, or methanecarboxylic acid), dissolved in water, including a lowamount of water such as 99 percent acetic acid. Acetic acid, e.g., insolution, is available in a range of concentrations of acetic aciddissolved in water, including very high concentrations of at least 95,98, or up to or in excess of 99 weight percent (weight (grams) pervolume (liter)) acetic acid in water (and is sometime referred to as“glacial acetic acid” in the substantial absence of water). An aceticacid solution of any useful concentration, including a substantiallynon-aqueous (99 percent acetic acid) ingredient, may be used as aningredient to prepare an etching composition as described, by combiningthe acetic acid with other ingredients such as hydrofluoric acid(aqueous solution), hydrogen peroxide solution, etc., as described. Theacetic acid ingredient can contain any concentration of acetic acid thatwill be effective to combine the acetic acid ingredient with the otheringredients to produce a useful etching composition as described,containing a desired amount of dissolved acetic acid.

A useful or preferred etching composition as described can contain anyuseful or desired amount of dissolved acetic acid. Preferred etchingcomposition can include a relatively reduced amount of dissolved aceticacid as compared to previous etching compositions that contain acombination of HF, AA, and H₂O₂, when described on a basis of dissolvedmaterials of the etching composition. For example, a useful etchingcomposition may contain less than 50 parts by weight dissolved aceticacid based on 100 parts by weight dissolved materials in thecomposition, such as an amount in a range from about 5 to 45, from 10 to40, or from 15 to 35 parts by weight dissolved acetic based on 100 partsby weight dissolved materials in the etching composition.

These amounts of dissolved acetic acid in an etching composition aredescribed as being present at a time at which, or soon after which,hydrogen peroxide is combined with dissolved acid materials to form a“point-of-use” composition. In use, when hydrogen peroxide is added toan aqueous solution that contains dissolved acetic acid, the acetic acidand the hydrogen peroxide can react to produce per-acetic acid.Advantageously, the per-acetic acid is believed to be effective inselectively etching silicon-germanium from a microelectronic devicesubstrate surface that also contains silicon, and, when present in aneffective amount at a time of initiating an etching step, the per-aceticacid is believed to be effective in reducing the amount of time for theetching step to achieve a silicon-germanium etch rate that is 90 percentof the maximum etch rate of the etching step.

The etching composition, in addition to the hydrogen fluoride, dissolvedacetic acid, and dissolved hydrogen peroxide, may also contain an amountof dissolved formic acid (i.e., CO₂H, aminic acid, formylic acid,hydrogen carboxylic acid, hydroxymethanone, and sometimes referred toherein as “FA”). The dissolved formic acid can be provided in theetching composition in the form of an aqueous formic acid solution as aningredient used to prepare the etching composition. Formic acid, in theform of an aqueous solution, is available in a range of concentrations,e.g., from 10 weight percent by volume, up to or exceeding 90 weightpercent by volume. An aqueous formic acid solution of any usefulconcentration may be used as an ingredient to prepare an etchingcomposition as described, by combining the aqueous formic acid solutionas an ingredient, with other ingredients of an etching composition, suchas with hydrofluoric acid (aqueous solution), acetic acid, hydrogenperoxide solution, etc., as described.

The amount of dissolved formic acid in an etching composition can be anyuseful amount, with preferred etching composition containing an amountof formic acid that is effective to improve one or more performanceproperties of the etching composition. Example etching compositions cancontain up to about 40 parts by weight dissolved formic acid based on100 parts by weight dissolved materials in the composition, such as anamount in a range from about 2 to 35, 5 to 30, or 10 to 25 parts byweight dissolved formic acid based on 100 parts by weight dissolvedmaterials in the etching composition.

These amounts of dissolved formic acid of an etching composition aredescribed as being present at a time at which, or soon after which,hydrogen peroxide is combined with the acid ingredients to form a“point-of-use” composition. In use, when hydrogen peroxide is added toan aqueous solution that contains dissolved formic acid, the formic acidand the hydrogen peroxide can react to produce per-formic acid.Advantageously, the per-formic acid (in combination with per-acetic acidalso present in the etching composition) is believed to be effective inselectively etching silicon-germanium from a microelectronic devicesubstrate surface that also contains silicon, and, when present in aneffective amount at a time of initiating an etching step, the per-formicacid is believed to be effective in reducing the amount of time for theetching step to achieve a silicon-germanium etch rate that is 90 percentof the maximum etch rate of the etching step.

The etching composition, in addition to the hydrogen fluoride, dissolvedacetic acid, and dissolved hydrogen peroxide, may also contain an amountof dissolved sulfuric acid (i.e., H₂SO₄, hydrogen sulfate). Thedissolved sulfuric acid can be provided in the etching composition inthe form of an aqueous sulfuric acid solution as an ingredient used toprepare the etching composition. Sulfuric acid, in the form of anaqueous solution, is available in a range of concentrations, e.g., from10 weight percent by volume, up to or exceeding 90 weight percent byvolume (e.g., 98 percent “concentrated sulfuric acid”). An aqueoussulfuric acid solution of any useful concentration may be used as aningredient to prepare an etching composition as described, by combiningthe aqueous sulfuric acid solution as an ingredient, with otheringredients of an etching composition, such as with hydrofluoric acid(aqueous solution), acetic acid, hydrogen peroxide solution, etc., asdescribed.

The amount of dissolved sulfuric acid in an etching composition can beany useful amount, with preferred etching composition containing anamount of dissolved sulfuric acid that is effective to improve one ormore performance properties of the etching composition. Without beingbound by theory, sulfuric acid is believed to catalyze the reaction offormic acid any hydrogen peroxide to produce per-formic acid, and toalso catalyze the reaction of acetic acid with hydrogen peroxide toproduce per-acetic acid. In the presence of sulfuric acid, the rate atwhich hydrogen peroxide reacts with acetic acid and formic acid toproduce per-acetic acid and per-formic acid is increased. As a result,when hydrogen peroxide is added to an aqueous composition that containsdissolved formic acid, dissolved acetic acid, and dissolved sulfuricacid, the concentration of per-formic acid and per-acetic acid willincrease more rapidly, as compared to the same combination of hydrogenperoxide with formic acid and acetic acid in the absence of the sulfuricacid. With respect to an etching composition as described, a higherconcentration of per-acetic acid and per-formic acid in the compositionat a time following addition of the hydrogen peroxide can beadvantageous, in that the increased amounts of per-acetic acid andper-formic acid can increase an etch rate of silicon-germanium, reducingthe amount of time required for an etching step to reach asilicon-germanium etch rate that is 90 percent of a maximum etch rateachieved by the etching step.

Preferred etching compositions can include an amount of dissolvedsulfuric acid that will increase performance of the etching compositionby reducing the amount of time required for an etching step to reach asilicon-germanium etch rate that is 90 percent of a maximum etch rateachieved by the etching step. Example amounts may be up to about 10parts by weight dissolved sulfuric acid based on 100 parts by weightdissolved materials in the composition, such as an amount in a rangefrom about 0.1 to 7, 0.5 to 5, or from 1 to 4 parts by weight dissolvedsulfuric acid based on 100 parts by weight dissolved materials in theetching composition.

Optionally, example etching compositions also contain an amount ofdissolved lactic acid (CH₃CH(OH)CO₂H, 2-hydroxypropanoic acid). Lacticacid is a water-soluble solid material and can be provided in theetching composition in the form of a solid lactic acid ingredient (e.g.,water-soluble powder), or as aqueous lactic acid solution of the lacticacid dissolved in water. The amount of dissolved lactic acid in anetching composition can be any useful amount, with preferred etchingcomposition containing an amount of dissolved lactic acid that iseffective to improve one or more performance properties of the etchingcomposition. For example, Applicant has identified that lactic acid inetching compositions and etching methods as described herein, can beeffective to improve etching selectivity of silicon-germanium relativeto silicon, when etching a substrate having both silicon-germaniumrelative and silicon on a surface.

Useful and preferred etching compositions can include an amount ofdissolved lactic acid that will increase performance of the etchingcomposition, such as by improving etching selectivity ofsilicon-germanium relative to silicon. Example amounts may be up toabout 20 parts by weight dissolved lactic acid based on 100 parts byweight dissolved materials in the composition, such as an amount in arange from about 0.5 to 17, 1 to 15, or from 3 or 5 to 14 parts byweight dissolved lactic acid based on 100 parts by weight dissolvedmaterials in the etching composition.

An aqueous etching composition as described, that contains dissolvedacid and hydrogen peroxide as described, can contain an amount of waterthat allows the etching composition to be prepared and used as describedherein. Example amounts of water can be in a range from 10 to 70percent, e.g., from 15 to 60 percent, such as from 20 to 55 weightpercent water based on total weight of etching composition.

An etching composition as described, in the form of an aqueous solutionthat contains dissolved acid materials and hydrogen peroxide, can beprepared by any method that will be useful to produce an etchingcomposition as described, containing dissolved acid and hydrogenperoxide materials in amounts and types described herein. By one method,aqueous or solid ingredients of the different dissolved materials can becombined any simply mixed to uniformity. For example, aqueous solutionsthat contain a dissolved material can be combined and mixed touniformity.

According to preferred methods, an etching composition can be preparedat a “point-of-use” composition by combining an aqueous solution of acidmaterials, with an aqueous solution of the hydrogen peroxide. Desirably,hydrogen peroxide may be held and stored separately from ingredientsthat contain an acid material. Also desirably, a single composition(e.g., aqueous solution, referred to as an “aqueous acids composition”)that contains all acid materials of an etching composition may bepreviously prepared and then combined with the hydrogen peroxide at apoint of use. The aqueous acids composition can contain, consist of, orconsist essentially of acid materials as described herein, dissolved ina single aqueous solution. An example aqueous acids composition cancontain, consist of, or consist essentially of hydrofluoric acid,dissolved acetic acid, formic acid, sulfuric acid, and optional lacticacid, all dissolved in water. Such an aqueous acids composition thatconsists essentially of hydrofluoric acid, dissolved acetic acid, formicacid, sulfuric acid, and optional lactic acid, all dissolved in water,can contain not more than 5, 2, 1, 0.5, 0.1, or 0.05 parts by weight ofdissolved or un-dissolved materials other than the identified dissolvedacid materials.

Referring to FIG. 3 , illustrated is a flow diagram of a preferredexample of a method of preparing a point-of-use composition (i.e.,aqueous etching composition, 16) from example ingredients that comprise,consist of, consist essentially of acid ingredients 3 and hydrogenperoxide ingredient (hydrogen peroxide solution) 14 (as well asadditional optional water 15). The acid ingredients can comprise,consist of, or consist essentially of: hydrofluoric acid solution 2,acetic acid solution (e.g., highly concentrated, 99% acetic acid) 4,sulfuric acid solution 6, formic acid solution 8, and optional lacticacid (solid or solution) 10. (Ingredients that consist essentially oflisted ingredients such as these are a set of ingredients that containsthe listed ingredients and does not contain any more than 5, 2, 1, or0.5 total weight percent of any other ingredient or ingredients.)

The acid ingredients 3 can be combined initially into an aqueous acidscomposition 12. This may be a composition that is prepared commercially,sold and transported to a customer, then used (after an optional storageperiod) by a customer in a step of etching a microelectronic devicesubstrate. A customer, at a point-of-use, can combine the aqueous solidscomposition (solution) 12 with an amount of hydrogen peroxide solution14, and optional distilled water 15, to produce point-of-use composition16 containing dissolved acid and dissolved hydrogen peroxide ingredientsas described herein. Within a short period of time after combing theacid ingredients 3 (e.g., aqueous acids composition 12) with thehydrogen peroxide solution 14, the point-of-use composition 16 can beused in an etching step at etching system 20. Etching system 20 may beused to perform any desired type of etching step on microelectronicdevice substrate 22. As a single example, the substrate 22 and etchingstep may be as shown at step 3 of FIG. 1 of the Examples, herein.

An etching composition as described may be prepared and packaged forstorage and sale as single-package formulations or as multi-partformulations that are mixed at or before the point-of-use. One or moreparts of a multi-part formulation may contain any combination ofingredients or dissolved materials that when mixed together form anetching composition as desired. Preferred etching compositions can beprepared for and packaged as a multi-part formulation or multi-partproduct that includes one part (i.e., one separate composition) that isthe aqueous acids composition that contains dissolved acid materials anddoes not contain hydrogen peroxide. The aqueous acids composition can bepart of a multi-part formulation that includes the aqueous acidscomposition and a separate hydrogen peroxide solution, which containshydrogen peroxide in an amount and concentration that allows directmixing of the hydrogen peroxide solution with the aqueous acidscomposition to produce an etching composition that contains desiredamounts of all dissolved acid and hydrogen peroxide materials. Thehydrogen peroxide composition may be sold in combination with theaqueous acids composition, or may alternately be provided separately toor by a customer, i.e., user of the etching composition. Optionally, theconcentrations of materials of single- or multi-part composition may beconcentrated, meaning that the composition contains an amount of waterthat is reduced relative to the amount of water that is to be includedin an etching composition at a point-of-use. Accordingly, a user of aconcentrated composition can combine the concentrated composition withan amount of water (preferably deionized water), e.g., 1, 2, 4, 5, 7, or10 volumes water per volume of concentrated composition, to form theetching composition having a desired amount of water, and desiredconcentrations of dissolved materials, for use.

The etching compositions are useful for methods of selectively removingsilicon-germanium material from a surface of a microelectronic devicesubstrate, relative to silicon. containing material using the siliconselective composition is contemplated. Methods of etchingmicroelectronic device substrates are known in the semiconductorfabrication arts, and can be performed on known and commerciallyavailable equipment. Generally, to etch a substrate to selectivelyremove a material at a surface of the substrate, etching composition canbe applied to the surface and allowed to contact surface structures toselectively remove certain of the structures, chemically. The etchingcomposition can be applied to the surface in any suitable manner, suchas by spraying the etching composition onto the surface; by dipping (ina static or dynamic volume of the composition) the substrate intoetching composition; by contacting the surface with another material,e.g., a pad, or fibrous sorbent applicator element, that has etchingcomposition absorbed thereon; by contacting the substrate with an amountof the etching composition in a circulating pool; or by any othersuitable means, manner or technique, by which the etching composition isbrought into removal contact with the surface of the microelectronicsubstrate that contains silicon-germanium and silicon. The applicationmay be in a batch or single wafer apparatus, for dynamic or staticcleaning.

The conditions (e.g., time and temperature) of a useful etching processcan be any that are found to be effective or advantageous. Generally,etching composition is contacted with the surface for a time that issufficient to selectively remove silicon-germanium, with the etchingcomposition being at a temperature that is effective for selectiveremoval of the silicon-germanium. The amount of time for an etching stepshould not be too short, because this means that an etch rate ofsilicon-germanium may be too high, which can lead to reduced quality ofa microelectronic device at the end of an etch step. Of course theamount of time required for an etch step is preferably not unduly long,to allow good efficiency and throughput of an etching process andsemiconductor fabrication line. Examples of useful times for an etchingstep may be in a range from about 5 minutes to about 200 minutes,preferably about 10 minutes to about 60 minutes, at temperature in arange of from about 20° C. to about 100° C., preferably about 25° C. toabout 70° C. Such contacting times and temperatures are illustrative,and any other suitable time and temperature conditions may be employedthat are efficacious to achieve the required removal selectivity.

After completion of a desired amount of selective etching ofsilicon-germanium, etching composition that remains on a surface of anetched microelectronic device can be removed from surface by any desiredand useful method, such as by a rinse, wash, or other removal step,using water. For example, after etching, a microelectronic devicesubstrate may be rinsed with a rinse solution of deionized water,followed by drying, e.g., spin-dry, N₂, vapor-dry etc.

The inventive etching compositions and methods can be particularlyuseful for selective etching of silicon-germanium, as a sacrificiallayer, from a substrate that contains structures of silicon andgermanium. In one example, the substrate contains multiple alternatinglayers of silicon and silicon-germanium. The inventive etchingcomposition and methods can be useful to laterally etch thesilicon-germanium material from between layers of silicon. The remainingstructure includes silicon nanowires that can be useful for preparing afield-effect-transistor (FET) of a microelectronic device. The term“nanowire” is used herein in a manner that is consistent with themeaning that this term is given in the semiconductor and microelectronicdevice arts. Consistent therewith, a silicon nanowire can be anano-scale structure made of silicon, e.g., monocrystalline silicon,which may be doped or undoped, and which may have dimensions thatinclude a cross section (width) in a range from about 20 to 100nanometers, e.g., 25 to 50 nanometers, and a longer dimension (e.g.,length or height) that may be in a range from 100 to 400 nanometers,e.g., from 150 to 300 nanometers.

The inventive compositions and methods, in addition to being useful toprepare nanowires as described, that can be included for example in afield-effect transistor, will also be useful for preparing otherstructures, including three-dimensional silicon structures (e.g., on aninsulator), silicon-on-nothing structures, and various other complextwo-dimensional and three-dimensional silicon structures that will beuseful as part of a microelectronic device, by use of the inventiveetching compositions to selectively remove silicon-germanium, as asacrificial material, from a substrate that contains silicon-germaniumand silicon.

EXAMPLE

Selective removal of SiGe has been used to remove sacrificial materialto generate advanced device structures such as silicon nanowires andsilicon on nothing (SON). These devices are fabricated by epitaxialdeposition of a layered structure followed by patterning and selectivelateral etching to generate a 3 dimensional structure. This is shownschematically for a nanowire application in FIG. 1 :

-   -   Step 1: An epitaxial stack of Si and SiGe is deposited.    -   Step 2: These are patterned with a standard lithographically        generated mask and directional etch.    -   Step 3: An isotropic etch is used to laterally etch away the        sacrificial SiGe material leaving behind a silicon nanowire.

One non-limiting example of a method for using an inventive compositionand etching method of the present description is illustrated at Step 3of FIG. 1 , involving an etching step for removing sacrificialsilicon-germanium from an epitaxial stack of Si and SiGe. An effectiveetch process to selectively remove the sacrificial SiGe can be one thatis highly selective to SiGe removal relative to Si removal. It isdesirable to use SiGe with low germanium content so that latticemismatch and therefore dislocation density is minimized in the resultantSi nanowires. Reducing lattice mismatch by using sacrificial SiGe with alow germanium content results in a greater challenge in achieving ahighly selective SiGe removal, because SiGe with low Ge content isbecomes very similar chemically to pure silicon. It is also desirable tohave etch rates that are not strongly dependent on crystal orientation.

Previously, for processing different microelectronic devices, selectiveetching of SiGe relative to Si (to prepare non-FET, non-nanowirestructures) may have been performed using an isotropic dry etch usingHCl, or by one of various potential wet etch approaches. One previouslydescribed method of selective etching involves a wet etch process thatuses an etching composition of acetic acid/hydrogenperoxide/hydrofluoric acid/water mixtures (see Cams et al., “ChemicalEtching of Si1-xGe x in HF:H2O2:CH3COOH,” Journal of the ElectrochemicalSociety, vol. 142, no. 4, pp. 1260-1266, 1995). Various shortcomings ofthe described methods include that a significant reduction in SiGe:Siselectivity exists when operating at a low Ge content of the sacrificialSiGe material, and that long times are needed to achieve stable etchrates after H₂O₂ addition. Moreover, for a substrate that includessilicon oxide or silicon nitride that is or becomes is exposed duringthe selective SiGe etch step, low etch rates for these materials aredesired. But a high HF concentration in formulations similar to thosedescribed by Cams et al. would be expected to make the described methodsand compositions unsuitable for these applications.

FIG. 2 shows an etch rate of Si_(0.75)Ge_(0.25) versus time aftermixing, for an etching composition of HPA (1:2:6) (HF:H2O2:AA) and of animproved etching composition of the present disclosure. If we define astable etch rate as changing less than 10% over the following 1 hour,the HPA formulation takes 2 hours to reach a stable etch rate, whereas astable etch rate is achieved in 30 minutes for formulation A.

The formulations and performance summarize at Table 1 shows performanceimprovements of inventive etching compositions relative etchingcompositions that are made of hydrogen fluoride, hydrogen peroxide,acetic acid, and water only.

Etching Formulations and performance, with formulations shown weightpercent of each ingredient.

(In parenthesis are reported parts by weight of each dissolved materialin a composition. The balance is H₂O. In this table entries marked nmwere not measured.)

TABLE 1 Ingredient concentrations in weight percent Si_(0.75) SiO₂(Parts by weigh of each dissolved material) Ge_(0.25): (thermal Time inLactic Formic Acetic Sulfonic Si Si_(0.75)Ge_(0.25): Si Etch oxide)SiN_(x) Etch Reach 90% Form- HF Acid Acid Acid Acid H₂O₂ Selec- Etchrate rate Etch rate SiGe Etch ulation (49%) (85%) (85%) (99%) (80%)(30%) tivity (nm/min) (nm/min) (nm/min) (nm/min) rate (mins) Form- 0.758 20 20 2 49.25 41 37 0.8 1.55 2.82  30 ulation A (0.368) (6.8) (17)(19.8) (1.6) (14.78) Form- 2 0 20 20 2 56 56 77 1.4 3.29 nm nm ulation B(0.97) (17) (19.8) (1.6) (16.8) HPA 1:2:6 11 67 22 23 37 1.7 nm nm 120(5.39) (66.33) (6.6)

In some embodiments, this disclosure includes a method of selectivelyremoving silicon-germanium from a surface of a microelectronic devicerelative to a silicon-containing material, the method comprising:providing a microelectronic device surface that includes silicon andsilicon-germanium, wherein the silicon-germanium has a formula: Six:Gey,wherein x is in a range from about 0.70 to 0.90, and y is in a rangefrom about 0.10 to abou 0.30, with x+y=1.00, providing an aqueousetching composition comprising: from 0.1 to 10 parts by weight hydrogenfluoride, from 10 to 35 parts by weight dissolved hydrogen peroxide,from 5 to 50 parts by weight dissolved acetic acid, from 2 to 40 partsby weight dissolved formic acid, from 0.1 to 10 parts by weightdissolved sulfuric acid, and from more than 10 to 20 parts by weightdissolved lactic acid per 100 parts by weight dissolved materials in theetching composition, wherein the aqueous etching composition is providedby combining the hydrogen fluoride, acetic acid, formic acid, sulfuricacid, and optional lactic acid to form a solution followed by combiningthe hydrogen peroxide and the solution to form the aqueous etchingcomposition; and contacting the surface with the aqueous silicongermanium selective etching composition for time and at a temperatureeffective to selectively remove silicon-germanium relative to thesilicon.

In some embodiments, this disclosure includes an etching compositioncomprising from more than 10 to 14 parts by weight dissolved lactic acidper 100 parts by weight total dissolved materials in the etchingcomposition.

What is claimed is:
 1. A method of selectively removingsilicon-germanium from a surface of a microelectronic device relative toa silicon-containing material, the method comprising: providing amicroelectronic device surface that includes silicon andsilicon-germanium, wherein the silicon-germanium has a formula:Si_(x):Ge_(y), wherein x is in a range from about 0.70 to 0.90, and y isin a range from about 0.10 to about 0.30, with x+y=1.00, providing anaqueous etching composition comprising: from 0.1 to 10 parts by weighthydrogen fluoride, from 10 to 35 parts by weight dissolved hydrogenperoxide, from 5 to 50 parts by weight dissolved acetic acid, from 2 to40 parts by weight dissolved formic acid, from 0.1 to 10 parts by weightdissolved sulfuric acid, and from more than 10 to 20 parts by weightdissolved lactic acid per 100 parts by weight dissolved material in theetching composition, wherein the aqueous etching composition is providedby combining the hydrogen fluoride, acetic acid, formic acid, sulfuricacid, and optional lactic acid to form a solution followed by combiningthe hydrogen peroxide and the solution to form the aqueous etchingcomposition; and contacting the surface with thesilicon-germanium-selective etching composition for time and at atemperature effective to selectively remove silicon-germanium relativeto the silicon.
 2. The method of claim 1, wherein the etchingcomposition comprises less than 1 part by weight hydrogen fluoride per100 parts by weight total dissolved materials in the etchingcomposition.
 3. The method of claim 1, wherein the etching compositioncomprises from 15 to 35 parts by weight dissolved acetic acid 10 to 25parts by weight formic acid per 100 parts by weight total dissolvedmaterials in the etching composition.
 4. The method of claim 1, whereinthe etching composition comprises from 1 to 4 parts by weight dissolvedsulfuric acid per 100 parts by weight total dissolved materials in theetching composition.
 5. The method of claim 1, wherein the etchingcomposition comprises from more than 10 to 14 parts by weight dissolvedlactic acid per 100 parts by weight total dissolved materials in theetching composition.
 6. The method of claim 1, wherein the etchingcomposition comprises from 10 to 70 weight percent water, per totalweight of the etching composition.
 7. The method of claim 1, wherein thesurface includes silicon nitride or silicon oxide.
 8. The method ofclaim 1, wherein the aqueous etching composition comprises less formicacid than acetic acid.